The present invention relates to an antenna apparatus for a communication device operating in the frequency range of between 800 and 3000 MHz, comprising at least one radiator which is Galvanically connected to one end a of a spiral conductor which in turn is connected to a transceiver.
The connection impedance to a transceiver of the type employed in so-called mobile telephones is often of the order of magnitude of 50 ohm. Depending, upon the design and type of radiator, its impedance may vary greatly, for example, within the range of between 100 and 1000 ohm. Thus, adaptation of the impedance is necessary.
In prior art designs and constructions, it is normal to build up an adaptation network of discrete components which are often placed on a circuit card in the communication device. Even if impedance adaptation in such designs and constructions may be satisfactory, these designs and constructions are generally expensive and suffer from high losses. Further, it is not possible, in this type of adaptation network, simply to include the antenna construction proper, as would be desirable since this would realise a simple and compact integral construction.
In mobile telephones in the stand-by mode, i.e., when the mobile telephone device is ready for receiving an incoming, signal, a small and compact antenna is further required, which, moreover must be mechanically durable and well protected. The degree of efficiency of such an antenna need not be sufficient to give complete range and transmission quality in the activated state, i.e., during talks. In order to realise a higher degree of efficiency in the antenna, use is often made of a retractable antenna which is employed in the activated state. Such a construction also presupposes the incorporation of an adaptation network between the antenna/antennas and the transceiver. There is a serious need in the art that all of these components can be downscaled to miniature and given good mechanical protection.
Problem Structure
The present invention has for its object to realise an apparatus which obviates the problems inherent in prior art constructions. Thus, the present invention has for its object to realize an antenna apparatus which may have one or two radiators and which has an integrated adaptation network, in which the adaptation network has a high degree of efficiency, is mechanically stable and extremely space-saving. The present invention further has for its object to realize an apparatus which is simple and economical in manufacture.
Solution
The invention relates to an antenna apparatus for a communication device operating in the frequency range of between 800 and 3000 MHz. The antenna apparatus is of the type having at least one radiator which is galvanically connected to one end of a spiral conductor, which, in turn is connected to a transreceiver at a connection point. The apparatus is characterized in that an earthed conductor extends along the extent of the spiral so that substantially all ofthe capacitance formed by the position of the earthed conductor is distributed along the spiral conductor.
In one aspect of the invention, the connection point is located on an opposite end of the spiral spaced away from the radiator. In another aspect, the connection point is disposed between the ends of the spiral.
In yet another aspect of the invention, the spiral and the transreceiver are galvanically interconnected with one other. Also, the axial direction of the spiral can be substantially parallel to the longitudinal direction of the radiator.
Preferably, the spiral is substantially of helical configuration and the earthed conductor is disposed concentrically in the spiral. An air space can lie between the earthed conductor and the inside of the spiral. In another embodiment, a sleeve of dielectric material is disposed about the earthed conductor with the spiral being wound on the sleeve.
In a first embodiment, the spiral is substantially helical in configuration, while the earthed conductor is disposed concentrically in the spiral.
In a second embodiment, the spiral is substantially planar, which also applies to the earthed conductor which has an outer contour approximately adhering to the outer contour of the spiral.
Further advantages will be attained according to the present invention if the subject matter of the present invention is also given one or more of the characterizing features as set forth in appended subclaims 4 to 15.